text:
When airspaces adjoin vertically, which airspace class does the shared flight level or altitude belong to?
Airspaces have a lateral and vertical boundary, which results in airspaces adjoining other and thus having a shared vertical boundary. Which airspace class do these shared vertical boundaries belong to?
Example:
Dortmund's (EDLW) control zone is a class D from GND/SFC to 2500ft MSL, on top of this control zone is a TMA airspace class D from 2500ft MSL to 4500ft MSL thereafter class E from 4500ft MSL to FL100and above that we have class C airspace from FL100 to FL660.

(Image Source: www.skyvector.com - Map Data: skyvector, ARINC, OpenStreetMap)
If an aircraft wants to occupy 2500ft MSL, 4500ft MSL or FL100, which airspace class are they in?

According to ICAO Annex 11 - ATS (Air Traffic Services)PDF, the less restrictive airspace is in effect on shared boundaries:

Note.— Where the ATS airspaces adjoin vertically, i.e. one above the other, flights at a common level would comply with
  requirements of, and be given services applicable to, the less restrictive class of airspace. In applying these criteria, Class B
  airspace is therefore considered less restrictive than Class A airspace; Class C airspace less restrictive than Class B
  airspace, etc.

Unless national regulations in the country's AIP are in contradiction or the national AIP does not list any information on this, the ICAO regulation will apply.
In the above example, the altitudes or flight level would be considered:
2500ft MSL: Class D airspace
4500ft MSL: Class E airspace, since class E is less restrictive than class D
FL100: Class E airspace, since Class E is less restrictive than class C
Related questions:
What is the difference between “flight level” and “altitude”?
What is the difference between the airspace's classes (for non-pilots)?

One exception to this is the boundaries of U.S. class A airspace, where aircraft at 18,000 feet AMSL (the lower boundary with class E airspace) or at FL600 (the upper boundary with class E airspace) fall in class A airspace, despite class A being more restrictive than class E.  EDIT: I realise that the original question was tagged "easa-regulations"; however, SentryRaven's answer cites general ICAO rules, which is what this comment is responding to.


text:
Is it OK to decorate a log book cover?
I'm a student pilot and am thinking about putting a tasteful decal on my log book, if for no other reason than to identify it as my own.  Is that OK, or would that be frowned upon?  Thanks.

Welcome to aviation.SE! For questions about regulations and/or what's considered acceptable, it's usually best to tell us which country or regulator you're asking about. Regulations and local practices are different everywhere.

@Pondlife, thanks for the heads up.  I'm flying in the Unite States.

@RyanJ Thanks for clarifying that. I've added the [faa-regulations] tag to your question since you specified you're asking about the U.S.

Out of curiosity, why does this question have an off-topic vote? I don't see what's off-topic about a question about maintaining logbooks.

I don't belive there is any regulation against it. Keep in mind you may need to show the book to officials at some point so keeping it professional is not a terrible idea

(1) Persons must present their pilot certificate, medical certificate,
  logbook, or any other record required by this part for inspection upon
  a reasonable request by -
(i) The Administrator;
(ii) An authorized representative from the National Transportation
  Safety Board; or
(iii) Any Federal, State, or local law enforcement officer.

The FAA is more concerned with what you log than what's on the cover of your book. I can't say I have ever seen a log book with a bedazzled cover but I'm sure they are out there. If you are talking about putting a decal that says "Ryan's Log Book" across the cover, that's fine, but a giant glow-in-the-dark unicorn sticker might get you some looks although technically OK.

Yeah it's a personal document.  Something that looks professional should be fine.  Teenage Mutant Ninja Turtle stickers could be a problem, career wise, going forward.

What is wrong with unicorns?

@bogl For a pilot, I'd expect a pegasus to be more appropriate, but to each their own?

If the decorations (stickers, bedazzling, etc.) can be removed later, it's a complete non-issue.  I wouldn't do anything permanent, though.  Making a removable cover, as another answer suggests, and decorating that seems an obvious solution.

@bogl Nothing is wrong with unicorns, it's purely a question of where they belong. If your heart surgeon broke out your medical records from a Lisa Frank Trapper Keeper, you might be forced to consider whether they're suitably qualified for the role and whether they take the related responsibilities seriously.

@J... Some people would argue that grass / astro turf belongs on the ground; but then this comes along.  Unicorns very clearly should be on books - unless they're orange imho, in which case more orange is better.

@aCVn: There's a flying unicorn meme going around.

I thought pilots were supposed to have pin-up girls.

My mother used to wrap my books when I was a kid in school for me. I don't know much about aviation and how this logbook looks, but maybe it's doable to use some kind of a "protective cover" that can be taken off anytime, in case you have to show it on official occasions?
Beside making your own from book protection paper, kitchen shelf paper, newspaper or non-sticky plastic foil, you can buy pre-made covers in different sizes. Have a look at a stationery shop, bookstore or at a school supply store. The foils and pre-made covers are available in transparent and different colors and with or without printings (for example maps).

While helpful information, this doesn't actually answer the legal aspects of the question and would be better off as a comment.

@FreeMan I think "Sidestep the legal issues and do it this way instead" is a perfectly valid answer.

@DavidRicherby fair point. It may be a "valid" answer, but not necessarily a "good" answer.

@FreeMan Sometimes, a good answer is one that doesn't actually answer the exact question posed by the OP, but solves the problem that question intended to address (aka XY Problem).

It all depends upon how your logbook will be used.  If you expect a professional career in aviation, then I would keep it within the envelope of what that community would expect.
Another thing to consider, you can have multiple logbooks.  For example, I have a separate book for gliders, glider towing and rotorcraft.  When instructing, I keep a lesson record, which covers instruction details, evaluation and logged times.  Those are summarized on a spreadsheet which I update periodically.  My work flying and my personal flying have separate logs as well.
The FAA inspectors seem happy with my record keeping and appreciate the segmented logs.  Things like night currency, instrument currency, glider currency, are recorded in the rear of the books and can be carried from book to book.
My multiple logbook implementation is not for everyone, but I mention it because if one wanted to have something radically unique, you might do so in a separate book.  As an example, early in my flying career, I noted the names of people I took up on rides, or had them sign my book.  Later, I decided to stop that practice when a significant other started reading the logbook.
But to be clear, your logs need only be a reliable record which you can readily use for FAA compliance, negotiating rentals, employment or whatever.  Many pro pilots I know used spreadsheets, and their company issues a record for company activity.  Similar in the military.
In summary, do what you want, but you may wish to maintain a more conventional presentation if you expect to be pursuing activities where your logbooks might get reviewed for employment or other activities.

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text:
Why do landing gear bays in commercial aircraft not have a fire extinguishing system?
Landing gear bays in modern commercial aircraft have fire detectors installed, but there is no fire extinguishing/suppression system in this area.
What is the logic behind having fire detection in this area when we don’t have extinguishing?
Why doesn't this area have fire a extinguishing system like other unpressurized areas like engines and APUs.

I wonder if it has to do with the fact that the engines and APU have a supply of flammable liquids going to them. Where as the landing gear bay only has the less flammable rubber and fire-resistant hydraulic fluid. If the rubber catches fire, you can extend it away from the aircraft body, exposing it to a 200 knot wind.

When your landing gear is on fire you are most likely on the ground, at which point it's more practical to wait for ground crew to come and extinguish the fire, although you need to know a fire has started in order to call for help.

@user3528438 Wheel well fire detection is about a fire in the enclosed space of the wheel well itself, i.e. with the gear retracted. It wouldn't detect hot brakes on the ground unless they were thermo-nuclear hot. Temperature sensors on the brakes would detect that condition, but that's separate from wheel well fire detection.

@RalphJ not necessarily. A leaking hyd tube on the top part of the gear may cause a fire to propagate in the wheel well. And some aircraft are very low: https://cdni.rt.com/files/news/1f/1f/90/00/9.jpg . But yes, most of the times with gear extended the fire is outside the gear bay.

Cost/Weight/Complexity, the usual reasons why you avoid to add another systems. But let's analyse if you really need it.
Easy to prevent
From the data of this Boeing document:

at least 62% of the wheel well fires are caused by applying excessive grease
at least 11% of the wheel well fires are caused by hydraulic leaks
at least 3%  of the wheel well fires are caused by incorrect application of solvents

From the fire protection standpoint the landing gear is a quite simple device: maintenance staff should pay attention where and how much grease they put, pay attention where solvents are put, and the only flammable liquid is the hydraulic fluid. An engine is much more complex, you have many flammable fluids (fuel, hyd, oil), many pipes and extreme forces, which make the maintenance error and engine damage more probable. Then, causes can also be external (like bird strikes). This makes an engine fire event probability much more higher.
Moreover, most of all events of wheel well fires appear after landing (i.e., after braking), which is still a serious problem, but not as serious like in-air fire.
Rare
Wheel well fire are 10x less probable than engine fires and 1.5x less probable than APU (source):

There were only 2 fatal accidents related to wheel well fires: Propair Flight 420
 and the Nigeria Airways Flight 2120. In both cases pilots were unaware of the fire and they didn't take any countermeasure.
Easy to solve
Just put the landing gear down. The >= 200 kts air does the rest. If it doesn't work, at least the most flammable materials (rubber, hyd pipes) and the heat source are now outside the aircraft frame and it will take more time to reach the wheel well, so you have more time to land.
Since wheel well fires are caused by high brake temperatures, the procedure is even usually applied before the fire actually exists. For example, the HOT BRAKES procedure of Airbus requires to lower the landing gear (and turn on the brake fan, if available) as soon as the brakes become overheated, potentially preventing in this way the fire event.

Your article is talking about brake fires, not fires in the wheel well itself, which is what the OP is asking about. Either way, though, "put the gear down" is the solution. Which would also, to the OP's question, disperse any extinguishing agent across the sky, removing its utility for fire protection.

@RalphJ Fire detection is there for fires caused by brakes (the only thing can reasonably be a source of ignition in the wheel well). Clearly, any other component of the aircraft can be cause a fire in extreme situations, but you don't have detectors/extinguishers everywhere, the OP was asking related to fire detectors in the wheel well.

The article doesn't really contribute to an answer -- it's all about "how to prevent" rather than what to do when they occur.  Most of the brake fires occur after landing (and some before takeoff), where wheelwell detection wouldn't matter.  To the extent that you get a fire in the wheelwell, it was most likely caused by dragging brakes, which the article omits from their discussion, since its entire focus is on maintenance practices.  The really germane part of the answer is the last part: put the gear down.

The OP didn't ask "what to do when they occur"... Deciding whether a protection system is added or not on the aircraft is a combination of factors during the design phases, that take in account maintenance procedures, costs, event probability, and alternative solutions (i.e.., lowering the landing gear).

There is no fire protection for wheel wells because any extinguishing agent would be immediately dispersed into the atmosphere as soon as the most important step for a wheel well fire, lowering the landing gear, is accomplished.
It's more important to get the tires outside the aircraft immediately and avoid containing the fire in a small space where it can do damage. Instead, let the airstream remove heat & any spraying hydraulic fluid.
Gear wells aren't sufficiently air-tight that allowing the fire to consume all the O2 is an effective response.

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text:
How to do the base turn course reversal?
Can anyone tell me how to do the base turn course reversal? Please. I'm afraid it might be asked of me in my Checkride and my instructors haven't taught me that. Please.

Why aren't you asking your instructors about it?

Fixed it for ya.

Not a bad idea to broaden you understanding on a forum like this because opinions and techniques vary, but you really need to ask the person you hired to prepare you for the checkride.

If your worried something will be on the checkride (which is practical) you need to seek out more practical instruction on the maneuver.
Procedurally this site offers a good explanation:

Base turn consists of:

a specified outbound track and timing or DME distance from a facility; followed by
a turn to intercept the inbound track

The outbound track and/or the timing may be different for the various
  categories of aircraft. Where this is done, separate procedures are
  published.


text:
Are there other examples of Brown-Stigler incident?
I have just finished reading A Higher Call and wondered if there are other cases where a pilot showed his mercy to the foe when they are in desperate situation. Looked through several B17 related-webs, forums, and made web scrap but found none. I guess there might be some, but maybe only written in memorial of pilots.

Fantastic story. Worthwile to note that (wikipedia source) "Stigler himself flew 487 combat missions, downing 28 planes while himself being shot down 17 times (he bailed out six times and landed in a damaged plane 11 times)." (from https://portraitofwar.com/tag/jg27-franz-stigler/ ).
Being shoot down 17 times. Surviving 17 times. Air-combats for him were like a videogame :D !


text:
While descending some pilots put local pressure long before reaching transition level?
Isn't this risky?
I thought once they pass transition level they should change to local pressure...
But is this not risky to put local pressure qnh before... risky in terms of separation wheter vertically or horizontally.

How would it affect anything horizontally?   If they are cleared down to an altitude below the flight levels then they are allowed to pass through all altitudes between.

Standard pressure is set above transition level. If you used local pressureway above some airplanes would be flying at different altitudes thus potential for risk of trafic or obstacles @Jim

Good.  Carry that thinking even further…

We are talking about descnding here, and the possible risks involved in using local pressure qnh above the tranition layer .(since when airplanes are above transtion layer standard pressure 1013.25hp reference system is used....) having different references provides problems. An airplane 3000 ft might collide with a 4000ft ...I mentioned not only vertically but also horizontally due to the fact that airplane can converge you from any direction ...hope this clarrified my point @Jim

So you are descending and have been cleared to do so.  You’ve set and are holding a vertical speed.  Does fiddling with the knob on the altimeter affect anything about the flight path?

Not sure if it affects the flight path or not but we are talking about safety here. Setting local pressure above the transition level I believe is a problem since you will not have the correct reference system needed. Traffic might be an issue, obstacles as well...(if not many planes nearby it maybe not an issue, at the end of the day they are many other system in an aircraft to avoid impacts...but why risk possibility. What if  its a busy airspace or many planes next to you climbing descending cruising....@jim

Yosef, I added some explanation to my answer to help you gain insight into the (perceived) safety issue that Jim is trying to lead you to discover for yourself.  Please let me know if that clears it up for you.

There is no risk in changing the altimeter at any time during the descent, as long as it is correct by the time you level off at your proper assigned altitude.
During the descent your displayed altitude may either be behind or ahead of whatever it would display if you were to level off above or below the transition.  But that doesn't matter because you are not leveling off, you are in a descent and your altitude is constantly changing.
If you were to receive modified instructions to level off before the transition and you have switch settings early you would need to switch back.  Otherwise, the vertical and lateral airspace around your descent would have already been verified clear by ATC before issuing the descent clearance.
The only practical effect is instrument lag:  Your altimeter may indicate a different altitude than another aircraft, (that already has adequate lateral IFR separation!) as you fleetingly transition through that same altitude.  It is a temporary condition, of extremely short duration, and is not a safety concern.

... and the lag issue is not really an issue. ATC is required to ensure separation from all other IFR traffic at ALL altitudes between the altitude you are departing and the altitude you are cleared to.  They do not watch your altitude and clear other traffic through your flight path at altitudes that you have already passed through!  Also, ATC does not see the altitude displayed on your altimeter, Mode C transmits an unencoded altitude which does not vary no matter what altimeter setting you dial in.

When you fly on autopilot (i.e. most of the time) and ATC tells you to "climb FL230", you dial 23000ft and 1013hPa into the computer and wait until it levels off at the correct altitude. Why would you postpone pressure setting until midway through the climb? That gains you nothing and creates the risk that you forget about it. Same for descent.

@RainerP. is your question directed at me, or the OP?

Yosef you are correct in the sense that setting local QNH before transition altitude during descent may be risky in the rare occasion the clearance to descent is abrubtly changed to an altitude above the transition level. In this case the plane's altimeter would read "wrong" unless the crew remembers to correct the altimeter setting.
Some may think this kind of situation is unlikely, but nevertheless it is possible. A plane may make a navigation error prompting ATC to halt your descent. Unforseen traffic may emerge (emergency, high priority military etc.) making it necessary to halt your descent.
Whatever the procedure pilot chooses to use for descents, it should contain memory item to check for correct altimeter setting when levelling off. If the changing of altimeter setting (well) above or below transition layer is based on SOP, usually a checlist but could also be a requiered memory item, it's ok, as the SOP's would likely contain altimeter setting checks for all actions relating to vertical movements. If, however, the QNH adjustment is done against SOP out of habit or for convinience, it is a potential safety issue.

Actually, this scenario is possible, but the consequences described are not possible. If an approved descent was halted by ATC, and acknowledged by the Pilot, the pilot would reset the altimeter setting as appropriate (depending on the new altitude requested by ATC ).  If there was no response from the pilot (radio failure or whatever), ATC would immediately be responsible for ensuring separation from all other IFR traffic until communications was re-established.

I can only speculate as to how this is dealt with in SOP's, but just as you described, the premature setting of QNH brings an extra step to this kind of situations, and is therefore not KISS. Let's say you are cleared from FL200 to 6000ft,  you set QNH. Something happens and ATC commands to stop descent at FL180. There is a chance you forget to reset altimeter, and end up at not FL180, unless the altimeter check is on checklist or a memory item for you.

Well, If the individual responsible for doing something he/she is required to do by standard operating procedure does not do it, and that causes a problem, yes that would be bad. But, for this very reason, as I mentioned in another comment, the altitude reading on the altimeter is Not what is transmitted by Mode C. If you are flying along at 18,000 on your local altimeter setting, The ATC controller will see that on his screen, and you will likely get a call from him/her to fix it.

Let me reiterate my point: setting QNH at, say, top of descent, adds an unnecessary hole in the slice of cheese. I've seen my fair share of cluttered checklists that had unnecessarily out of place items. Luckily most of them got cleaned out over time. I do, however see your point and I've slightly edited my answer @CharlesBretana

and, to be explicit, I can unequivocally say your point is also a valid one. But it also applies in the much more common scenario where the descent is not canceled. If you wait til you level off at your lower altitude, and get busy doing other things during descent, and then forget...   Changing QNH when starting the descent "gets it done" at altitude, when you are likely less busy.

And having the wrong QNH is potentially way more of an issue on your approach than it is at cruise altitude.

Fully agree @CharlesBretana


text:
What is gimbal error in DGI compass gyroscopes?
I'm unable to find an explanation of gimbal error in a Directional Gyroscope Indicator (DGI) anywhere. Can someone please explain what this is?

Short answer
The gimballing error is the mechanical error introduced by the cardan design of a gyro DI. A cardan joint is linear only when its input and output axes are aligned.
In the gyro DI axes are aligned when the wing is level. When the wing is banked the non linearity of the transmission makes the compass map lead or lag behind the gyro wheel.
Because there is a non linearity, the gyro precession rate is also changed. While the lead/lag error disappears when the wing is level again, the precession rate error is permanent.

Details
There are two main errors on an directional indicator gyro:

friction drift,
gimballing error.

Drift is due to friction occurring in the rotation axis of gimbals. This is analog to drift observed in inertial platforms. Drift is slow and continuous. Gimballing errors occur during large turns at steep angles and are related to the mechanical design of a gyro, which is similar to a cardan joint. In a cardan, input and output velocities are equal when the input and output axes are aligned (0° angle), but differ as soon as there is a misalignment. See this page for a full explanation. The relationship between output and input is this one, computed for a few misalignments:

Non linearity of output vs input in a cardan, left image source, right image adapted from source
We can see the error is null for input angles multiple of 90°. The gimballing error has two aspects.
Recoverable mechanical non linearity
The wheel axis of rotation (not the spining axis) and the output axis are aligned when the aircraft is level. In this case the wheel orientation is exactly transmitted to the map (middle image below).

Gimballing error when the aircraft is banked. Source for left image
In a turn the outer gimbal axis is banked with the aircraft while the wheel still rotates around a vertical axis (right image above). Because the two gimbal axes are no more aligned, the cardan design introduces an error on the output axis. The compass map starts leading/lagging behind the actual wheel orientation change.
The error can exceed 10°, but is not permanent. It disappears when the aircraft is returned to level flight.
Non recoverable precession error
The cardan non linearity creates accelerations on the wheel. A gyro is sensitive to these accelerations, they perturb its precession rate. A permanent error is introduced in the instrument. A 360° turn may introduce as much as +/-1° error. Fortunately these errors don't have the same sign, and partially cancel the previous ones. I don't have the TSO (C5e) related to DI certification, but I think 1° is a requirement.
More about DI errors.

thanks this was a good answer.

I've accepted it. Can you please answer this as well https://aviation.stackexchange.com/q/90280/35047


text:
Would it be better to limit AOA in F16 jet in dogfights more than it is now?
Would limiting the angle of attack to a maximum of 13 degrees by the fly by wire system help pilot gain advantage over his/her enemy during aerial one to one combat?

I cannot understand this question, please edit so that it becomes clear what the information you seek is.

The headline kind of makes sense, the rest, not so much.

I asked due to the fact that there is a decaying of the speed at higher AOA if the F16 pilot want preserve their speed to not go beyond this value of their AOA if must do ACM

Ok. First: you are relying on people knowing what ACM/BFM is. If you just wrote "maneuvering", it would immediately be more obvious for anyone what this might be about. Second: the order in which you have placed the words it and is makes the sentences statements, not questions. I do realize english is not your native language, but this is a very basic thing. Third: what does 11/13 degrees mean? So basically you are stating here that AoA should be kept under 0.8461538462 degrees to minimize loss of speed.

The AOA is the angle of attack  (airflows which will meet the wing) The value I give is maximum 13 AOA not more than and speed about 400knots.

@jpe I think he means 11 to 13 degrees, which would be better written as 11-13.  He's talking about setting the fly-by-wire to avoid high angle of attack to limit induced drag, I think.

Zeiss Ikon Exactly what you said.

It depends on what you are trying to do.  I suggest researching energy-maneuverability theory.

George, dog fights are about energy management, not necessarily  AoA.  Please read up on John Boyd's works regarding wing loading, Q, and energy management.

Air to air combat is not about speed, you simply cannot outrun a modern missile. Not even the older ones... While it is true than maintaining speed = maintaining kinetic energy, to use speed as a winning advantage in aerial combat you would have to be stupid fast, like SR-71. Going that fast requires high altitude, and there you would definitely want to limit your AoA (load factor), IIRC limit for Blackbird was something like a deviation of a couple of degrees at cruise, so maneuverability no longer applies when using the outrun tactics.

This is actually a seed of a good question because it brings out the basic strategies of aerial combat. I will try to rephrase it a bit later, so that it is clear, and portrays the problem George Geo is facing.

@GeorgeGeo I rephrased the question, please check if it is ok for you. I also voted for reopening.

Everyone knows that if you limit the angle-of-attack, you limit drag.  The same lift for less drag sounds like a win-win.  Yes the flight control programmers should it write it into the control law program that any desired lift vector should be generated at not more than 13 degrees angle-of-attack.  (Translation: the question appears to have lost track of what variables are constrained by what other variables.)

Or is the question simply whether limiting the aoa to a maximum of 13 degrees would be beneficial?

On further reflection the question as currently stated seems clear enough.

There is a real gain to increase the AOA at your discretion as a pilot  at higher speed  (because the drag will kill the speed) in dogfights?

Up untill a certain AoA, lift increases, enabling faster turn rates. The ability to utilize max lift is a definite advantage in aerial combat. If your plane's AoA is limited, your enemy will very quickly outmaneuver you. And you will be shot down.

related, if not dupplicate: Are fly-by-wire fighters protected in AoA?

First of all, the F-16 flight control computer DOES limit AOA. But this is avoid loss of control due to exceeding Maximum Controllable AOA, not to prevent energy loss.   The energy is there to ENABLE high AOA maneuvering when it is necessary by the pilot to either defend against a threat, or achieve a valid weapons employment solution. It would be foolish to stop the pilot from maneuvering hard enough to defeat an Air-to-air missile, just so he has more energy when he dies.

I removed the CAT 1 and CAT 3 part lately edited into the question. It had no connection to the original question.

Of course not. The pilot needs to be able to command the maximum turn capability of the aircraft when it is necessary, for, among other things, to defend against a missile that has been launched at him/her, to maneuver the aircraft into a weapons launch envelope, or to slow the adversary line-of-sight-rate for a high angle-off (heading crossing angle) gun attack.
And, actually, The F-16 flight control computer DOES limit AOA. But this is avoid loss of control due to exceeding Maximum Controllable AOA, not to prevent energy loss. The energy is there to ENABLE high AOA maneuvering when it is necessary by the pilot to either defend against a threat, or achieve a valid weapons employment solution. It would be foolish to stop the pilot from maneuvering hard enough to defeat an Air-to-Air missile, just so he has more energy when he dies.

I feel like I have the right answer. This will not be possible because the deployment of the elevators is not the same at  lower altitudes as the highest level of service celling.The rarefied air need more deflected control surface to have a better answer to the pilot maneuvers


text:
use the KiGass to reduce the heat of engine
I'm researchigng a spitfire crash near my home town 1944 .  The pilot did not survive the crash. Now I'm writing his story. The pilot reported engine trouble. During my research I found followin data:

His wingman reported later (quote) "I saw black regular streams of boost smoke comming from the
aeroplane, indiciating he was priming his way".
There is a change that the radiator was hit by FLAK and was leaking, resulting in a cooling problem and raising the engine temperature.
the radiator was black, mostlike set on fire

Trying to find possible cause of the crash, I have questions (I'm not an engineer)

can priming the engine (kigass) reduce the engine temperature to avoid overheating
can a cooling radiator set on fire? For example after being hit by flak or because of (extended) priming ?
best regards

What is KiGass?

Please pretend your question is going to your editor and [edit] your question for spelling, grammar and clarity...

Kigass is the name of the company that made primer pumps for Spitfires.  Apparently, "Kigassing" became slang for injecting fuel into the engine in that manner.

Bullet number 2: change or chance?

His wingman reported later (quote) "I saw black regular streams of
boost smoke coming from the aeroplane, indiciating he was priming his
way".

The point is that the engine was apparently not getting any (or sufficient) fuel through the normal means, so the pilot was using the primer to deliver fuel to the engine.  Not that the pilot was trying to cool the engine by priming.  The "regular streams" of "boost" (perhaps should read "black"?) smoke from the engine were due to the primer delivering a rich mixture, not due to a fire that the priming was intended to extinguish.

can a cooling radiator set on fire?

Ethylene glycol is combustible.  See for example https://www.cdc.gov/niosh/ershdb/emergencyresponsecard_29750031.html#, click on "emergency response", "fire fighting information".

This is about what I was thinking.

If the account was a transcript of a verbal debriefing then "blue" might be a better interpretation of "boost".

Although glycol is flammable, it's mixed with water in engines, including the Merlin XII by 1939 (per Wikipedia.  Normally there's more water than glycol because water has higher specific heat capacity (only slightly higher volumetric heat capacity).  Glycol alone, however, has a higher boiling point (lots of relevant  data at engineering toolbox, but unfortunately not the flash point of a mixture

... but  see DSIAC - even pure glycol, not used in the Spitfire by '44 would be a low risk, and with 30% in water, no risk

It's notable that running rich causes cooler cylinder temperatures than running lean, so injecting extra gas into the cylinders, even if they were already running, would cause cooler cylinders and (I think) lowered exhaust gas temps as well.  For a modern example of this phenomenon, piston engine airplanes are typically run full rich during takeoff to reduce the high cylinder temperatures caused by full power.

To your specific questions:
First, dumping fuel into an engine by priming to cool it by evaporation does not work. In an operating engine a rich mixture runs cooler than a lean mixture, but this is because the lean mixture burns slower and exposes the cylinder to high heat longer. The result is measured in tens of degrees in cylinder head temperature while the flame in the cylinder is ~2000 centigrade. If the pilot was indeed priming the engine, he was trying to keep it running in the belief it was not getting fuel.
Second, it was not coolant from the radiator catching on fire. The spitfire radiator is wing mounted near the belly and nowhere near the engine, so black residue here was either always there or may have been smoke residue from an already burning engine.

Also, though ethylene glycol is slightly flammable any water mixed in needs to be driven off before it will ignite. The spitfire uses 70% water 30% EG, so this is not easy to do without a nearby, already burning, heat source.

An initial review of a few papers examining both antifreeze and pure ethylene glycol seem to indicate that there is a low risk of the coolant being either an initial fire source or a primary fuel source.  As expected, the water and the phase change required to evaporate it is a strong deterrent to igniting the coolant due to heat losses, and since ethylene glycol has a boiling point of 388 °F (198 °C), the water will preferentially be evaporated first before significant ethylene glycol vapors can be generated.

You did not specifically ask for the cause of the crash but if a pilot reported engine trouble in an aircraft emitting smoke after possibly being hit by flak, it is likely the engine had mechanical damage and either oil or fuel was starting to burn. The reference to your "boost smoke" statement to gather context would be helpful, as to my knowledge this is not a thing.

Running richer mixture will lower the engine temperature to a certain degree, but I'm not sure, given the information availlable, this is why priming was used in this case. As quiet flyer suggested, the pilot may have attempted to feed the engine fuel by priming to keep it running.
The "boost smoke" may also have been a small fire in the engine bay, since the radiator was covered in soot. Then again, are you sure the radiator was not painted black? This is sometimes used in automotive applications to increase heat transfer in low flow conditions (black surfaces both emit and absorb heat more efficiently).

Black is no better than silver in radiation at engine cooling temperatures. This heat is radiated at mid IR wavelengths, outside the visible spectrum. Black absorbs visible wavelengths better than silver which is the source of the misunderstanding.

IR emission, unless temps are very high, is negligible compared to heat rejected by conductive/convective transport. It's why you insulate buildings for convective heat loss, not IR, and painting heat exchangers black to get their emissivity near 1 has no detectable effect, more than offset by the insulation of the paint. The same reality is a problem for the global warming narrative. IR absorption by greenhouse gasses from earth's surface is less than 10% of energy absorption by the atmosphere. It's nearly all conduction/convection and water evaporative transport.

I've seen studies/tests where there is a measurable difference between black and bare metal emissivity, I'll try and find them. I'll reiterate these were automotive applications involving stationary air (iirc).

As noted by Pilothead, the radiator is not inside the 'engine bay' so that part makes no sense.

There is, as it turns out, plenty of evidence that painted surfaces radiate heat with greater intesity than polished metal. Now, radiator rarely are polished, so in that sense my comments are senseless (pun intended). but anyway.


text:
Can a wind gust below the rotor affect the lift force in a helicopter?
If a helicopter is hovering and a very strong, narrow and focused wind gust comes from the front and passes few feet below the rotor blade without touching the fuselage or any part of the aircraft for that matter, would the helicopter lift or altitude change in any way?

If it helps, another way to put it, imagine if you had a very powerful leaf blower with a rectangular nozzle of about 6 feet width X 1 foot height, and you are aiming to the helicopter downwash at a height of about 3 feet down from rotor blades. The red lines in the image represent the wind from the leaf blower.
PS: The helicopter is in-ground-effect hover.

Is the gust acting upon the rotor?

no, is a very narrow and focused gust few feet bellow the rotor. Another way to put it. Image if you had a very powerful leaf blower with a rectangle nozzle of about 8 feet width X 1 foot height, and you are aiming right trough the helicopter downwash about 3 feet down from rotor blades.

In-ground-effect or out-of-ground-effect hover?

@RalphJ good question. In-ground effect. It would be interesting to see your answer in both cases though, if it is not too much to ask.

OGE I'd expect that it wouldn't affect things.  IGE, I'd suspect that it could, but I'll let a rotorhead explain the real answer.

Wind cannot be "focused."  Since wind is not an object and has no boundaries, there is no meaning to wind "touching" an object.

I mean you can even visually see it in a wind tunnel with smoke.

Yes the horizontal gust influences lift - initially it reduces lift, since the gust lowers static pressure $p_s$ underneath the rotor.
The helicopter hovers on top of a column of air accelerated downwards, with the rotor experiencimg total pressure $p_t$ equals $p_s + \frac{1}{2} \rho V^2$. All in a nice equilibrium, until an external differential wind gust is exerted. Which adds local velocity, thereby reducing static pressure. Velocity direction is [arallel to the rotor and therefore the increase in dynamic pressure does not contribute to lift. Easy to verify: just blow over a tree leaf resting on the ground, and it will float up.
If the gust continues for a while, the airflow direction through the rotor will change plus the lower static pressure underneath the rotor will suck in more flow through the rotor. The situation will now be more like that in forward flight, which provide more lift for a given power setting, as stated in this answer.

Perfect, we have two opposing theories. I summon @PeterKämpf

Yep, I thought this was going to be a easy question, someone must have done this experiment before like in a wind tunnel or something. I can't believe no one has tested this before, like a aircraft manufacturer or something.

@Gabe I think this is not much of an interest, other than purely academic and wind tunnel time is costly. IRL one will not  meet the conditions you've described. It was fun to think about though

"...just blow over a tree leaf resting on the ground, and it will float up." but if you slide a plate with zero AoA through the air it will not produce lift, right?

@Jpe61 Correct, because in that case total pressure is equal on both sides of the plate. In the case questioned, an external factor causes increased air velocity on one side, parallel to the lifting surface., which reduces static pressure on that side while not increasing upwards dynamic pressure. And of course what happens over time after the first initial burst is more complicated.

I understood the question such that the gust itself is not directly in contact with the rotor disk. Hence it shoud have no effect on the lift equation? I readily admit this is way beyond my pay grade, and as you wrote this is actually very complicated if all things are to be considered.

Lift would momentarily increase.
I have reasoned this in the following manner:
The rotor produces lift by accelerating air downwards. The air mass then proceeds down, and in ground effect is diverted sideways, when out of ground effect, it continues downwards untill it eventually loses momentum due to turbulence.
Now, if we suddenly push a new slice of air with no vertical speed right under the rotor, the air pushed down by the rotor will run into this air and start pushing it down. While the new air layet is being accelerated downwards, it locally increases the pressure of the air mass above it. This would essentially be the same as if the ground was getting closer to the rotor.
I also envision that the increased lift is most prominent in the portion of the rotor disk that is facing the gust. The portion "downwind" of the gust will encounter less pressure rise since the air was already pushed into downwards motion by the upwind part of the rotor.
So if the gust came form the front and passed under the right side of the rotor disk, the nose of the helicopter would tilt up and the helicopter would roll to the left.

Caveat! The answer above is pure reasoning, no science behind it. I'm quite good at seeing stuff like this with my mind's eye, but I'm not always right

If a helicopter is hovering and a very strong, narrow and focused wind gust comes from the front and passes few feet below the rotor blade without touching the fuselage or any part of the aircraft for that matter, would the helicopter lift or altitude change in any way.

Basically this confined gust blows only on the wake beneath the rotor without touching the rotor itself. If so, then the answer shouldn't be complicated.
Just like in a fixed wing, also behind a rotating blade a wake gets shed from the trailing edge. The wake mainly possesses a downward movement which is termed downwash. The following picture (from this paper) shows this downward-moving wake in a good way:

Note that the wake shed by the tip rolls up behind the blade creating a tip-vortex, just like behind a fixed wing. But unlike a fixed wing, as soon as the blade makes a complete rotation around the hub, it bumps into its own wake; and if there are more blades on the hub, then it bumps into their wakes as well. Note for example how, in the following picture, the blade at 270° bumbs into the downwash shed by the previous blade at 0° (figure from this paper):

This "swirling" environment that a blade encounters in its rotation is called inflow and has a quite complicated nature but, in general, its average movement is downwards. That implies that the AoA seen by the blade gets decreased due to the inflow.
Now, if we perform your experiment and blow this downward inflow away, what we could expect is, on average, a smaller decrease in the AoA seen by the blade so that the thrust should increase.


text:
Is there ground effect flying below an infinite 2D plane as opposed to above one?
People talk about wing tip vortices and say things like the ground acts as an aerodynamic mirror. What (if any) difference would there be for a wing flying underneath a 2D plane? As in the picture below:

The uppermost plane is flying at an altitude well outside ground effect. The middle one is flying in ground effect, and the bottom one in the hypothetical situation with a plane on top of the plane (pun intended).
Source of the picture, edited to suit the question:
http://www.aerospaceweb.org/question/aerodynamics/q0130.shtml

You don't really need an infinite plane, just one that is large compared to your wingspan.

@Sanchises - I think the OP meant continuous instead of infinite. One long enough in the longitudinal axis to be present throughout the entire flight. I doubt there would be a ground effect advantage from the reduction of wing-tip vortices. But, would there be any other type of advantage like changes in pressure above the wing? And, how close would the aircraft have to fly in order to take advantage of this benefit?

Correct. Size/dimensions not exactly relevant. I'm just talking above vs below or ground vs ceiling.

I added a picture diplaying the situation as I imagine the question means it. If I am mistaken, please remove my edit to the question.

In computational fluid dynamics (CFD), ground effect can be simulated by flying two airplanes / wings in mirror formation (the lower one inverted).
That mirrored wing is only a mathematical trick. By distorting the flowfield in an identical, albeit inverted, way, the effects of the lower wing cancel out those of the upper wing in the plane of symmetry, and vice versa. This way, the flowfield on both sides looks exactly like one where the plane of symmetry cannot be crossed by the flow, just as the ground cannot inhale or expel air.
Now, with the more precise description: Yes, there is also a ground effect for the plane flying below a hypothetical ceiling. Of course, it would help if the vertical tail would not stick up, for minimum distance and maximum effect. Just as the ground stops the downward movement of the wake, a ceiling will prevent air from filling the space left by the downward movement of the wake, so the wake will stick to the ceiling. Call it the ceiling effect, if you will. In both cases the induced drag drops and the center of pressure moves a bit backwards. I wager to predict that the drag reduction over distance relative to wing chord is the same as in "regular" ground effect.
Proof: Fly a model helicopter indoors and get it up to the ceiling. You will notice that it will get stuck there and needs much less power to stay airborne. The rotor blades are like wings, and due to the rotor position on top of the craft, the ground effect is very noticeable. In order to get the helicopter unstuck you must reduce power a lot, such that the helicopter will drop like a stone.
In CFD, this can readily be proven by using the trick described above, only now with both wings / airplanes flying inverted to their original orientation for the ground effect calculation.

The way I read the question, he's talking about flying in free(ish) air under a continuous solid ceiling.  I have to think there would be some effect, I'm just not sure what that would be...

Yes as above, I'm talking about a 2D plane above the wing not below it. That's why I said plane instead of solid.

This is an interesting thing to explore. If lift is the product of moving a package of air down, and a large part of that package is above the wing (I read somewhere long ago that the displaced air extends about half a span above the wing), you might think that lift is drastically reduced once the wing gets close enough to a solid surface above and as it gets close, at some point it would stop climbing if held at a constant AOA.  So, what happens when you try to fly a model, or hover a drone, right against the ceiling I wonder...

@ZeissIkon. Thank you for explaining this. I thought immediately of the old CFD trick for ground effect simulation. But the same trick can of course be done with both airplanes inverted. The results are identical: Less drag and a backward shift of the center of pressure.

Is it really the same situation? In one configuration your preventing the wake to develop while increasing pressure on the lower side. In the other you create some sort of venturi effect accelerating the airflow even more on the suction side. In addition if you come to close to the ground on top is there any possibility to choke the flow and thus stall the wing ?

@John K I have noticed when flying drones into enclosed spaces they often move up a couple of inches. Of course this is very unscientific but it did help form my thoughts before asking this question.

I remember as a kid flying prop-copter toys -- pull a string and a propeller with a ring on the tips would fly off the handle.  Flown indoors, and sufficiently near level, these would "stick" to the ceiling for up to several seconds.  I was fascinated, and used to pester my mother to stick the thing to the ceiling again and again.  Seems like loss of lift close to an overhead surface isn't a huge issue...

The situation with the ground above your aircraft is very similar to F1 cars front wing. And even if the airflow around it is much more complicated than the airflow around and airplane wing, ground effect seems to have a great impact.

The front wing is inarguably the most important part of a Formula 1 car, despite only providing between 20 and 30% of total downforce it is responsible for the quality of airflow reaching the rest of the car; generate too much downforce from the front wing and rear downforce will be reduced. Too much upwash in the front wing wake can stall the suspension members, or even cause the flow to separate at the front edge of the sidepod, which can adversely affect the rear wing and diffuser.

While the front wing profiles are shaped like a conventional wing section, a cambered upper and lower surface producing downforce, its force characteristic are dominated by ground effect, namely the Venturi effect in the convergent-divergent path under the wing, such that the air flowing on the lower surface of the wing is multiple times faster than would be the case is the wing were suspended high in the air.

https://www.f1technical.net/features/21667


text:
Why do fabric skin constructions not show up much in larger single engine piston aircraft?
I noticed that many ultra-lights use fabric skin but are not seen much in GA aircraft, especially compared to carbon fiber? Many skin makers advertise that it can handle that sort of weight. Is this due to difficulty manufacturing, weight, smoothness of surface, strength of material or other factors?

are you asking about fabric covering? The expression "stretched skin" does not exist and sounds as if you confused it with "stressed skin", something that is very common in GA aircraft.

@PeterKämpf Thanks! You are right. I just updated the question

Not that I have an answer anyway, but it seems to me that you need to be a bit more specific. The term GA covers many types of planes, some of them really quite heavy, powerful and fast in a context of fabric-covered planes. Your local CEO hotshot on his/her Citation or Gulfstream, for instance, is flying under general aviation rules. So what do you include in your category of "larger" GA planes?

@Monolo Thanks! Clarified it

Very few aircraft have only a single piston!

Fixed it. Although this was way more fun when the headline was in its original form.

This answer assumes that "GA" means "little piston planes."
Aluminum (or non-fabric) aircraft tend to "hold up" better against the elements.  I would not store a Stinson 108 outdoors but would not think twice about storing a 172 (or Cirrus) on an open air tiedown.  The fabric covering requires a great deal of care compared to the metal (or composite) skin of most GA planes.
Fabric planes must be re-covered every few decades, more frequently if neglected.  This is a non-trivial operation with a price tag to match.  This typically involves reconditioning the now-exposed structure which adds significant cost.  Re-covering and painting a Cub (small plane), for example, can cost an owner tens of thousands of dollars. Stripping, treating, and painting a "metalized" Cessna 120 (similar to a Cub) is a much easier, faster, and cheaper task.
Another consideration is the availability of aluminum.  Aluminum was declared a strategic material in WW2 and, as a result, a great deal of energy was allocated to increase production.  With the war over and the infrastructure in place to produce a lot of aluminum cheaply, why adhere to an antiquated manufacturing process requiring a painstaking level of detail when lower skilled labor can use cheap aluminum to mass produce high quality planes?
In short, fabric planes typically require more care and attention than their stressed skin cousins.  They also require somewhat specialized and skilled labor to build and maintain.  This generally translates into higher costs for everyone involved.
I'm sure there are technical reasons for the shift away from fabric but I'll let Peter (or another technical expert) comment on those.

How small is a little piston? Sorry, I'll get mi coat...

This should be understood as a supplement to @acpilot's excellent answer. All his points are valid and correct, and I just want to add a few more.
Fabric covering is easy to build and hard to maintain. In the early days, when engines were heavy and less powerful, a wooden airframe with fabric covering was the fastest, lightest and easiest way to get airborne with the skill set of a carpenter. Later, welded steel tubing became popular especially for fuselages because it makes it easy to introduce big loads locally. Again, fabric covering was the easiest to give the truss an aerodynamic shape. Maintenance was hardly considered, given that the lifetime of early aircraft was a few years at best and a more likely few minutes only.
With better engines, wing loading and speed increased. Now the weight disadvantage of a plywood or even metal skin diminished, and with the increased experience of both designers and operators, aircraft enjoyed a much longer life. Only now the disadvantage of fabric covering showed up, but it was still kept even in WW II airplanes (the fuselages of the Hawker Hurricane and the Vickers Wellington were fabric-covered), especially in the control surfaces so their balancing mass could be kept low. With the danger of flutter at high speed, fabric covering became unacceptable for the main structural members of fast aircraft: Only the torsional stiffness imparted by a plywood or metal skin made fast flight possible.
Low wing loading designs like gliders and motor gliders kept their fabric covering even longer, and some modern ultralight / microlight designs still use it today. Glider designers would probably still use it were it not for the much better surface quality possible with composites. Being fair-weather aircraft, gliders are less affected by the obvious disadvantages of fabric covering.

Thanks for the answer! Would have accepted them both if it was possible

Another point for the use of fabric with ultralights is that many of them are portable.  At the extreme, think of your typical hang glider, which is broken down, rolled up, and carried home on a roof rack.  Can't really do that with a metal skin :-)

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
What is this black star symbol in the picture below? If it means a hazard with no altitude information, what kind of hazard is that?
What is this black star symbol in the picture below? If it means a hazard without altitude, what kind of hazard is that?

A separate picture of similar symbol with altitude information:

What does the 5280’ mean?

The altitude of hazardous obstacles with a beacon.

So why did your question say “without altitude”?

Because there is no altitude specified for the star symbol in the first picture I shared. These are two separate pictures. I shared the second picture to indicate what the star symbol represents in the Jeppesen manual.

Got it.  For questions like these the airfield diagram is better than an approach plate.  Google earth is also your friend…

Not trying to pile on here, but to further my point, in the question linked below you included an airfield diagram for the same airport.  If you simply looked at it you would realize that the beacon is at the North East part of the airfield.  And please always include the airport identifier for specific questions like this.  Don't make us ask.

Your other recent question with airport diagram:  https://aviation.stackexchange.com/questions/95254/what-are-these-blue-lines-around-the-runway-at-the-airport-chart-that-i-marked-w

I don't think there is any doubt at all now that it is the beacon on the tower...

I will edit the question with a detailed airport diagram.

@757toga, or you should...  or Jamiec should...  or ___   ;)

That's the airport beacon light.


text:
If I get a speed restriction from ATC, at what point am I no longer obligated to comply with the restriction?
If a controller clears me for a procedure, and also says "...do not exceed ___ knots", how long does that restriction apply for?

Which country are you asking about? Rules may vary.

@757toga Both, I guess? Your answer is great though, thank you so much

@randomhead I was asking about the US, I definitely should have put that in the question.

You must maintain that speed until
ATC releases you from that restriction. When ATC want you to do something, there's a good reason for it, so we do as we are told. However, if you think they may have forgotten you, you can always ask


text:
Why are planes required to cruise at round flight levels only above 18000 ft of altitude?
AFAIK, planes flying at up to FL180 (18,000 ft pressure altitude) are allowed to fly at both round and semi-round altitudes (e.g. 15,000 ft or 15,500 ft). Planes flying above FL180 must fly at a round altitude (e.g. 28,000 or 29,000 ft but nothing in between). Why aren't planes allowed to cruise at semi-round flight levels above 18000 ft of altitude?

Where did you get this information? FAA - Altitude Assignment and Verification does not mention this at all (except for the well-known odd/even altitudes based on heading).

The examples it provides all end with an 0 too. But if I understand it correctly: in the USA you can cruise up to 3,000 ft (AGL it seems, not MSL) at any altitude, up to FL410 (41,000 ft MSL) the 1,000 ft intervals (e.g. at 37,000 ft) with exceptions and above FL410 in 2,000 ft intervals (does this mean you can't cruise at 42 or 43,000 ft above U.S. soil?) with exceptions.

So basically, the round intervals start above 3,000 ft AGL already, not above 18,000 ft MSL as in my question though that's the law above America.

@Giovanni -- not quite right re the US-- above 3000' AGL and below 18000' MSL, VFR traffic flies at "round" numbers plus 500' (e.g. 3500', 4500', 5500', etc) while IFR traffic flies at "round" numbers (e.g. 4000', 5000', 6000', etc).  Plus there's an additional rule about when flying on headings (actually ground tracks) from 000 to 179, VFR traffic uses the "odd" thousands (e.g. 3500', 5500'), and uses the "even" thousands for tracks from 180 to 359 (e.g. 4500', 6500').  See https://www.aopa.org/news-and-media/all-news/1999/july/flight-training-magazine/legal-briefing-vfr-cruising-altitudes

@Giovanni -- re the US again --the same "odd/even" separation based on ground track applies to IFR traffic too, at least below 18000' -- odd for 000 through 179 (e.g. 5000', 7000' ) and even for 180 through 359 (e.g. 4000', 6000')  -- see https://learntofly.ca/vfr-ifr-cruising-altitudes/  -- Not sure what happens at 18,000' and above, except that normally VFR traffic is not allowed -- (exceptions-- sailplane "wave windows", etc --)

@Giovanni -- so in the US, if you are just bouncing around VFR and maneuvering, not really cruising at any constant altitude, you'd be wise to avoid (or at least be extra vigilant around) the "round" thousands, because that's where the IFR traffic will be concentrated--

The question would be improved by saying what jurisidiction or jurisdictions you are interested in -- US?  europe?  both?  all?  etc.  (Really we should have held off w/ the answers till that was clarified)

@quietflyer No, you shouldn't have. Just all jurisdictions / international air law.

I substituted extreme with higher. For airplanes nothing under 50000ft should by no means be considered as an extreme altitude.

@Jpe61 Flights above 18,000 ft are called "extreme altitude", that's not my invention so don't point with the finger at me. "High altitude" is between 8,000 and 12,000 ft and "Very high altitude" between 12 and 18,000 I think. At 18,000 ft the sea level atmospheric pressure is halved (0.5 atm) so I don't think there's anything bad about the definition. Humans can't survive permanently above ~20,000 ft.

Oh, this is new to me, where is this defined? And it was not my intention to point fingers, it simply is a fact that 18000 ft is really not a very high by any standards. Wonder what the altitudes many airliners fly today, 40000ft, not to mention the altitudes reached by the U-2 and the retired SR-71, and the highest of all, A-12 (also ret.)   Maybe stupid, insane, mind numbing and ludicrous, respectively

How close together do you think they should fly?  500ft? 100ft?

@abelenky "Semi-round" would mean 500 ft, but I don't "think they should" fly at these gaps, I'm just asking why the rule is as it is.

@Jpe61 As of now I've found this: https://en.wikipedia.org/wiki/Altitude_sickness#High_altitude But there's also something called "ultra altitude" which is above 25,000' I think. As for your examples, you may even add the X-15, the SpaceShipOne and Two and the Space Shuttle, but from some point on we probably should call it "distance from the planet" rather than "altitude". :-)

@Giovanni you should note that the classification you are referring to is altitude from human performance perspective. From the viewpoint of air traffic, there is nothing extreme in 18000ft! If you tell a pilot you were flying at extreme altitudes, they are gonna think something along the lines of 60000ft.

@Jpe61 It counts in aviation as well because of the requirements of cabin pressurizations and rules like this. But I'll let the edit.

In general, the minimum vertical distance two IFR aircraft can be (if they are not separated laterally) is 1,000 feet. This allows for inaccuracies, for example due to:

altimeter error
instrumentation imprecision
pilot imprecision
turbulence
aircraft height (compare a Skyhawk, nine feet tall, with an A380, 79 feet tall)

while still making sure aircraft do not physically occupy the same 4D location.
In order to make things easier, especially in the non-radar control environment but also in the radar control environment, IFR aircraft cruise at distances that are 1000' apart (depending on their direction of flight). If, say, there was one flight at 4200' and another at 4600' and they were going to get close, the controller would have to issue a change in altitude to one or both planes, and then allow them to go back to their original altitudes. If they are instead at 4000' and 5000' then nothing needs to be done.
It is theoretically possible that the rule could be "All aircraft must cruise at xx,835 feet"—e.g. an eastbound plane at 15,835' and a westbound plane at 16,835' would be properly separated. But due to general inaccuracies and imprecision, as well as the way humans perceive numbers, it is much easier for the cruising altitudes to be "round." ATC only sees altitudes in hundreds-of-feet increments, and "steam gauge" dials may include ten thousand feet of readout in a dial only a couple inches in diameter. Using round thousands of feet is generally easier.
Then there are VFR aircraft. In most airspace there is no defined minimum separation between two VFR aircraft, nor even between a VFR aircraft and an IFR one. But it would still be very very bad for the two to occupy the same 4D location. So the rule is that VFR aircraft cruise "in between" at the half-altitudes, the x,500' altitudes.
Once in Class A airspace (in the US, FL180 to FL600) VFR is not allowed, with certain very limited exceptions, so there should be no aircraft cruising at FLxx5. It is still true that an aircraft at FL205 and one at FL215 are separated, but to make things easy and consistent the cruise altitudes are still round thousands. (Once you get even higher it is more difficult to maintain a steady altitude, I believe due to the reduced air density, and eventually the minimum separation increases to 2000'.)

To put it all another way: In the absence of any other traffic an aircraft can fly at whatever altitude the pilot likes. But when there may be traffic conflicts, it is prudent to ensure aircraft are separated by default, and that means using prescribed altitudes.

nice job of explaining the rationale behind the rules a little better there, I just kind of blurted them out-- : )

Re "To put it all another way: In the absence of any other traffic an aircraft can fly at whatever altitude the pilot like" -- the FAA might argue that point!  Just a thought

On the other hand, eastbound planes at 4572m and westbound planes at 4877m routinely fly past each other with no ill effects, despite the non-round numbers. ;-)

"while still making sure aircraft do not physically occupy the same 4D location." Well, the Pauli exclusion principle takes care of that quite handily.  It's really about preventing two aircraft from testing that principle.  Usually the attempt results in major unintended structural modification of the craft involved, typically because both craft are in something of a hurry when they arrive at the co-location in question.

Is the top of RVSM really because of difficulty in maintaining altitude? I just assumed that the RVSM rules stopped at FL410 because there wasn't enough traffic above that level for RVSM to be needed anyway.

It also offers some protection against wake turbulence from one plane to another and protects against cases of minor vertical control issues.

@reirab: I'm going off wikipedia here, https://en.wikipedia.org/wiki/Reduced_vertical_separation_minima#Historical_background, which cites https://www.icao.int/esaf/documents/rvsm/2010/afi%20riss/presentations.pdf

FL410 as top of RVSM may be because no one flies above that due to regulation… oxygen mask must be worn by one pilot above FL410. Concorde was exempted, certified before the rule went into effect.

This answer is specifically for the US--
Above 3000' AGL and below 18000' MSL (which is not the same thing as FL 180)1, cruising VFR traffic flies at MSL altitudes which are "round" numbers plus 500' (e.g. 3500' MSL, 4500' MSL, 5500' MSL, etc) while cruising IFR traffic flies at MSL altitudes which are "round" numbers (e.g. 4000' MSL, 5000' MSL, 6000' MSL, etc).
There's also a rule stating that when flying on magnetic courses (i.e. the intended magnetic ground track) from 000 to 179, VFR traffic will use "odd" thousands (e.g. 3500' MSL, 5500' MSL), and will use the "even" thousands (e.g. 4500' MSL, 6500' MSL) for courses from 180 to 359. See this source.  The same "odd/even" separation based on course applies to IFR traffic too, at least below 18000' -- odd for 000 through 179 (e.g. 5000' MSL, 7000' MSL) and even for 180 through 359 (e.g. 4000' MSL, 6000' MSL) -- see this source.
So in the US, if you are just bouncing around VFR and maneuvering, not really cruising at any constant altitude, you'd be wise to avoid (or at least be extra vigilant around) the "round" thousands, because that's where the IFR traffic will be concentrated.
The exact wording from FAR 91.159 specifying when VFR traffic should follow these prescribed cruising altitudes is "in level cruising flight more than 3,000 feet above the surface"... "except while holding in a holding pattern of 2 minutes or less, or while turning".  This language would not apply to extended "cruise" climbs or "cruise" descents, as well as all sorts of maneuvering flight beyond simple "turning" (e.g. practicing stalls -- or full-blown aerobatics).  Consider also that it's actually more efficient for a pilot to let his or her plane drift up and down a bit when passing through updrafts and downdrafts, rather than pulling the stick or yoke back to hold altitude in downdrafts, and putting the stick or yoke forward to hold altitude in updrafts-- the exact opposite of the strategy that a glider pilot would choose to maximize cross-country speed over an extended course.  This sort of variation in altitude would appear to take a plane outside of the realm of "level cruising flight".  Still, it would be wise to avoid the "round" thousands while flying in this manner, since that's where the IFR traffic will be cruising.
At the end of the day, a pilot must remember that there's a myriad of reasons an aircraft may be flying at an altitude other than the one prescribed by FAR 91.159 for extended level cruising flight.  And some of that traffic may lack a transponder.  "See and avoid" always!
In the US, VFR traffic essentially never is allowed to cruise at or above 18,000' MSL, but IFR traffic operating at or above 18,000' MSL will operate in reference to "Flight Levels" rather than actual MSL altitudes.  "Round" numbers will be used (e.g. FL 190, FL 200, FL 210.)  The east-west rule will apply here too -- airplanes flying with magnetic courses between 0 and 179 degrees will be assigned "odd" Flight Levels (e.g. FL 190, FL 210), while airplanes flying with magnetic courses between 180 and 359 degrees will be assigned "even" Flight Levels (e.g. FL 200, FL 220).
Footnotes:

Flight Levels are determined by setting the altimeter's pressure setting (Kollsman window) to the International Standard Atmosphere pressure of 1013.25 hPa (29.92 inHg), while actual MSL altitudes are determined (or at least closely approximated sufficient to satisfy regulatory requirements) by using the  pressure setting of a nearby airport.  Generally speaking, the actual height above ground of any given "Flight Level" shows much more variation, with changes in atmospheric pressure, than the MSL altitude reading obtained with the altimeter set for the pressure setting of a nearby airport, which should be a close approximation of the aircraft's actual altitude above sea level.  In the US, "Flight Levels" rather than actual MSL altitudes are only used at or above 18,000' MSL.  In contrast, in Europe, Flight Levels are used well below 18,000' MSL.

Really this answer was more about correcting a specific misconception in the question, than answering the "why" part of the question-- all the answers can work together; ASE doesn't discourage partial answers as I understand it--

I'm interested in the pressure altitude, the altitude above sea level pressure of 29.92 inHg (14.7 psi). As I understand it, FL takes the actual pressure at the plane's location into account or am I wrong?

@Gio, see this question. Also note that the US is a special case because the transition level and the start of Class A airspace are the same altitude; in the UK for example it is perfectly common to have a VFR aircraft at FL065. The two concepts are not related.

@Giovanni -- re your last comment -- deviations from standard atmosphere (i.e. high pressure or low pressure meteorological conditions) will affect the height of any given "flight level" relative to actual ground level, much more than they will affect the height relative to actual ground level of the msl altitude reading obtained w/ altimeter kollsman window set to pressure setting of a nearby airport.  So, which one is "taking onto account the actual pressure"?  Arguably it depends on how you look at it, you could make a case for either way.

I.e. , does "taking into account" mean that a compensation is made, so that meteorological variations don't affect the value, or does it mean that meteorological variations are allowed to affect the value?  Language can be tricky sometimes--

@quietflyer The atmospheric pressure at 40,000 ft MSL should be 2.73 psi. I understand Flight Level in the way that at FL400 you'd always fly in a 2.73 psi atmosphere, regardless of your actual altitude above sea level, right?

what about between 280 and 359 degrees?

@user253751 -- oops, thanks for catching that, fixed

@Giovanni -- re last comment-- correct

@quietflyer Very well. Thanks.

You probably got a mistake over the footonote. "even" Flight Levels (e.g. FL 210, FL 230). you probably crossed thoughts with odd numbers here even though you meant even ones (210 appears at the odd ones, too)

@masterX244 -- thanks, fixed.


text:
How would tiltwing aircraft pressurize their cabins?
For fix-wing aircraft, the pressurized air can travel from the engine through the wing and into the cabin. However, a tilt-wing aircraft, such as the CL-84 Dynavert (shown below), will have its wings "detach" from its fuselage. How would such an aircraft send pressurized air to the cabin?

https://commons.wikimedia.org/wiki/File:Canadair_CL-84.jpg

I fall to understand why the pivoting wing precludes transferring pressurized air to the fuselage. You don’t have to use rigid connections.

Given (except for the V-22)  you are talking about experimental aircraft, they may not be pressurized.

I went through the list of tiltwing aircraft on Wikipedia and couldn't find a single one that is pressurized. Are sure there is a pressurized tiltwing?

I don't think there is any tiltwing with a pressurised cabin. If there would be one, I don't see why it would need to be pressurised while the wing is tilted, since that typically happens only at low altitude during take-off or landing. It seems you are looking for a problem that does not exist.

I do not think this question deserves -1. Even though someone might not be familiar with rotary seals or flexible (high temp) pressure piping, it does not make this a bad question. Neither does the apparent misconception that pressirized tiltwings exist. This is an honest basic question about aircraft related tech.

It's pretty easy. Flexible ducting is readily available. Of course yours would twist in torsion, but it doesn't have to. It can be arranged to bend instead.
The wings are held on by a big, tough horizontal spar.  It's round because the wing rotates on it. It's hollow because that's strongest for weight.  Thus you are guaranteed to have a big, hollow, round pipe running from the fuselage to at least the mid-wing.
If the bearings could be sealed from blow-by, or if some leakage of bleed air through the bearings is tolerable, the bleed air could be run directly down the hollow spar.  Otherwise the spar could be "sleeved" with a plastic tube, which is designed to be OK with 90 degrees of torsion over 15 or so feet of its length.  The torsion of the tube would be spread down its entire length, which isn't asking a lot.

And presumably there would be tubing with similar issues for fuel and for hydraulic controls.

This is done in the engineering world all the time, using something called a rotary seal. installing one of these in a pipe allows the ends of the pipe to rotate relative to each other without losing pressure in the pipe.
Rotary seals also are used anywhere a rotating power shaft emerges from a gearbox or an engine block that has oil under pressure inside it, to prevent the oil from squirting out of the shaft hole.

I am asking about tilt wing aircraft though, wouldn't the pipe from the wing just simply be detached from the pipe on the fuselage when the wing is tilted?

no, the rotary seal would allow the wing to tilt while maintaining connection to the engine and the cabin.

But rotary seal just enables the end of pipes to rotate, i can't see how it works when most of the wing is separated from the fuselage. Is there anyway you can use a picture to illustrate what you mean?

the pipe runs through the pivot axis of the wing hinge, and the rotary joint is inside the hinge.


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Why do I never see any other planes in the sky whilst flying?
I was just wondering as I passed the airport this morning why, whilst we are flying, do I never see any other planes nearby? There must be millions of planes and millions of people flying each day, I appreciate the sky is massive but these planes must follow roughly the same routes so how is it that they never seem to pass by any other aircraft?

It's more like thousands of planes, and they typically stay at least a few miles apart. With the distance and relative speed between them, they can be hard to spot. That's why ATC works to keep them separated.

Not sure how often you fly but I see other airplanes every time I get in one, GA or commercial, and yes, while cruising. I guess being a pilot I've learned to look?

@fooot nope, 1000 feet is usually enough, as long as it's vertical.

Flying in a busy route in clear sky I was away able to see others airliners (or it's lights) just a few miles apart and hundred feets higher or lower flying in the opposite direction

@falstro that's what I meant by "typically"... passengers can't see straight up or down, and if they are only that close for a short period of time.

@jean I've seen that as well.  It's pretty startling when that happens, and it really gives you a sense of your speed.

@fooot no. But they can be half a mile away as long as they're 1000ft below, and it's not uncommon at all to spot aircraft in roughly the same direction, and they stay in plain view for several minutes.

I've often seen jets alongside the flight I'm on for long periods.  Typically about a mile apart horizontally and a couple of flight levels above or below. One of my favourite "spotting" opportunities is in a stack at Heathrow looking up and down in the turns.

@Tristan Yeah, it's really interesting when you meat another jet at an airway intersection. You suddenly get a much better perspective for how fast you're actually moving. However, if you want to guarantee you'll see another airplane, just fly into Atlanta. There will be at least 1 and often 2 more planes landing at the exact same time as you on a different runway and you'll fly parallel to them for the entire final. Also, flying over ATL at night, you'll see the huge swirls in the sky beneath you of the approach and departure patterns to the different runways.

I'd recommend trying again while on a night flight - commercial airplanes are usually well lit and flashing light beacons all over, which makes them somewhat easier to spot. But one still needs to actively look.

In my last flight to London Heathrow, arriving at about 19:00, I saw about a dozen or more airplanes in the last 60-90 minutes (when the plane was over France/Netherlands)

If you're not seeing them, you're not looking.
I see planes all the time when flying commercial.  Obviously, I see them a lot more when close to a major center, and a lot less when in the sparse parts of the Pacific Northwest (Montana, Idaho, Oregon, Washington).
I think spotting them may take some practice. Visually, a plane 10+ miles away is a very small dot, and easily missed.   Try looking for contrails and be sure to look at altitudes above and below you.  Scan the sky in narrow, 10°  concentrated "fields of view" to scan from left-to-right all the way across the sky.

"Scan the sky in roughly 10 degree segments making 18 different, concentrated "fields of view"" I want to fly as a passenger on an airplane that has 180° field of view! Usually only a pilot gets such a wonderful picture of the sky, at least in the air.

I was taught 10-degree segments during my flight training.  And from the cockpit, I can probably see a bit more than 180 degrees;   As a commercial passenger, you will see a lot less admittedly.

I think I have seen another airplane on just about every flight I've ever taken.

I think "you're not looking" may be a bit harsh. Your 3rd paragraph perfectly addresses why - "I think spotting them may take some practice".

It's also easier to see other planes at night, with the navigation lights.

If you look at sites like Flightradar24.com, you'll see aircraft following the same route, and close enough to allow each other being seen by passengers. Screenshot (look at the scale):

From my personal experience, seeing other aircraft is really common, as already commented and answered, even far from busy airports. I took this picture over Germany, the other aircraft is just a bit higher:

I let who is interested compute the aircraft distance from the size of the static wick. Actually there was a third aircraft in the background, still a common occurrence:

Nearby aircraft can be missed when there is no condensation trail. In general it's easier to spot an aircraft flying at a lower altitude, because Sun's light is reflected by the airframe.

There must be millions of planes and millions of people flying each day

At the time of the question there were about 100,000 commercial aircraft and 9 million passengers flying at a given time in the world. That's not a large number if we consider the size of the planet, but as you said they choose the same routes (for economical reasons). Airways can be very crowded and the absolute separation required for safety purposes is not so large (can be 1,000 ft, 300 m).

Nice photo, mins! Are those yours? How was that for a nice way of asking for attribution? :)

Aircraft are usually routed one in front of the other, often at different flight levels.
Situations where another aircraft would be flying alongside yours, where they would be easily visible, are fairly rare. They do happen though. I was flying from Chicago to Boston last Thanksgiving and there was another heavy alongside about 2000 feet below and 3000 feet to port.
If aircraft are on an intersecting airway, they will generally be several miles away, so they will be very small, and will usually be at different flight level.

That's not true, you DO see other planes in the sky. I fly very infrequently (on average probably 1 flight a year) but I've seen other planes in flight. I remember on one flight, my airplane entered a quite steep bank to the left, I was sitting by the right side window, and I saw another passenger jet fly past above me, it was rather close, probably a 1000ft altitude difference.


text:
Do I have any authority over airspace above my land?
With all this talk about drones flying around and delivering parcels for the merchant websites, I'm wondering from a "landlubber's" perspective, how much say I have over the airspace of my private land.
Now I know this question is a bit broad and quite difficult because it might differ from country to country and also depend on the size of the land, for instance a farm vs. a house in the city. It might also be interesting to know how it affects a piece of private land with a private runway.
But since it is sadly the norm these days for every country to follow Europe's lead eventually on these kind of privacy issues, Europe's might be the most relevant in the end. Any general insight from you all on this would be very informative.

I'm pretty sure that if you want to put anti air-air artillery in your backyard you should at least issue a NOTAM (besides having appropriate licenses)

I was more thinking about setting up an air traffic control tower which they need to ask for permission when passing overhead. :)

But since it is sadly the norm these days for every country to follow Europe's lead eventually on these kind of privacy issues, Europe's might be the most relevant in the end. Any general insight from you all on this would be very informative. - that's not even true...

Yeah, the Ukrainian rebels  really should've issued a NOTAM...

In Bernstein of Leigh v Skyviews [1978] 1 QB 479, the High Court of England and Wales held that, at common law, the right of a landowner to the airspace above their land was "to such height as was necessary for the ordinary use and enjoyment of his land and the structures upon it".
As another answer has suggested, the use of UK airspace is now regulated by statute.
Section 76 of the Civil Aviation Act 1982 says:

No action shall lie in respect of trespass or in respect of nuisance, by reason only of the flight of an aircraft over any property at a height above the ground which, having regard to wind, weather and all the circumstances of the case is reasonable, or the ordinary incidents of such flight, so long as the provisions of any Air Navigation Order and of any orders under section 62 above have been duly complied with and there has been no breach of section 81 below.

In other words, you may fly an aircraft at a height that is reasonable, subject to any specific regulations.
For example, rule 5 in schedule 1 of the Rules of the Air Regulation 2007 prohibits low flying in certain circumstances, such as below 1,000 feet over a congested area of a city, although there are various exemptions to those rules. For the detail, consult the regulations. Update: This is now rule 5 in schedule 1 of the Rules of the Air Regulation 2015.
What this means in terms of a landowner's right is that:

their rights do not extend beyond what is "necessary..." in accordance with Bernstein of Leigh whatever the specific rules on aircraft may say
additionally, the landowner's rights are restricted by the CAA and the rules made under it, so that an aircraft that complies with the rules and flies no lower than is reasonable etc does not commit a trespass or nuisance.

Welcome to Aviation.SE!

In the US you have, effectively, zero rights over the airspace above your land by default: Control of airspace is entirely delegated to the FAA, and they're super serious about it.
If you designate your land as an airport you can certainly establish a control tower and request an airspace designation from the FAA - whether or not they approve your plan depends on the existing airspace around you though: If your airport would create a problem for an existing airport you'd probably not be able to get an airspace designation for it, and it may even be classified as an objectionable airport.

This is probably a silly question, but, if you walk into my land, I have every right to kick you out. But if you come floating a few centimetres over ground, I cannot touch you?

@Davidmh Practically you can do whatever you want until/unless someone objects, but technically the FAA has jurisdiction over ALL airspace in the US (even class G "uncontrolled" airspace is under their administrative jurisdiction): As soon as you leave the surface they're the ones whose regulations you have to deal with. As nonsensical as it is that means someone operating a quadcopter 1 foot off the ground is technically the FAA's problem (nobody said the laws had to make sense!)

By the way, a question tag says EASA regulations. It is the European FAA.

@voretaq7 I'll be jumping when I rob a house next.

@yo' I think this means all those movies we've seen where people break into museums using helicopters to steal gems and such...  FAAs problem, totally.

Technically if you fly maybe you are FAA problem but once you touch the ground, you are in trouble with police.

"Judge rules man had right to shoot down drone over his house" http://www.cnet.com/news/judge-rules-man-had-right-to-shoot-down-drone-over-his-house/

The Supreme Court handled this issue:  https://supreme.justia.com/cases/federal/us/328/256/case.html

This will differ from country to country, but I will give an example based on the German law, so you can derive how countries can work with airspace.
In general, following BGB §905, the airspace above and ground below your property is also yours, unlimited.

Das Recht des Eigentümers eines Grundstücks erstreckt sich auf den Raum über der Oberfläche und auf den Erdkörper unter der Oberfläche.

But this is not the only relevant law, i.e. there are others that need to be looked at, such as those pertaining to airspace use in Germany, the LuftVG §1:

(1) Die Benutzung des Luftraums durch Luftfahrzeuge ist frei, soweit sie nicht durch dieses Gesetz, durch die zu seiner Durchführung erlassenen Rechtsvorschriften, durch im Inland anwendbares internationales Recht, durch Rechtsakte der Europäischen Union und die zu deren Durchführung erlassenen Rechtsvorschriften beschränkt wird.

The bold part basically says that all aircraft can use airspace freely, so technically, the drone/rc copter above your land is legal. If you want to claim you are an aircraft, irrespective of the size requirements, there is a lot of additional rules that need to be looked at, e.g. LuftVO §6

(1) Die Sicherheitsmindesthöhe darf nur unterschritten werden, soweit es bei Start und Landung notwendig ist. Sicherheitsmindesthöhe ist die Höhe, bei der weder eine unnötige Lärmbelästigung im Sinne des § 1 Abs. 2 noch im Falle einer Notlandung eine unnötige Gefährdung von Personen und Sachen zu befürchten ist. Über Städten, anderen dicht besiedelten Gebieten, Industrieanlagen, Menschenansammlungen, Unglücksorten sowie Katastrophengebieten beträgt die Sicherheitsmindesthöhe mindestens 300 Meter (1.000 Fuß) über dem höchsten Hindernis in einem Umkreis von 600 Metern, in allen übrigen Fällen 150 Meter (500 Fuß) über Grund oder Wasser. Segelflugzeuge, Hängegleiter und Gleitsegel können die Höhe von 150 Metern (500 Fuß) auch unterschreiten, wenn die Art ihres Betriebs dies notwendig macht und eine Gefahr für Personen und Sachen nicht zu befürchten ist.

The bold part states that over populated areas, a minimum safe altitude of 300m / 1.000ft must be maintained, unless you are taking off or landing with your drone. There is a plethora of other rules and regulations that need to be followed as well, another good SE question is this What is the maximum altitude allowed to fly a model plane/copter in Germany?

nice bit about the moon, but there's no need to make laws about it as Germany signed international treaties which say that nobody can own the moon :)

@jwenting Argh, you are right. Remove the section or leave for smile value? The section can refer to any celestial body, or do the intl. laws cover all planets?

This raises the question of whether considering things like the Tropic of Cancer and Tropic of Capricorn whether the moon ever really travel over Germany...

@jwenting, No space-faring country has ratified the Moon Treaty, and the Outer Space Treaty doesn't forbid claiming sovereignty over the Moon. Further, both treaties apply only to countries and not to individuals. (The last point was part of Richard Garriott's argument for claiming a portion of the Moon for himself after he purchased the Russian lunar rover.)

I guess that since this is German law, and the Moon cannot be claimed as German territory as per the OST, it is hard to argue that German law enables you to claim ownership of land on the Moon.

the moon can't be in zenith over Germany, the maximal latitude it can be at zenith is 23° (earth's axial tilt) + 5° (moon's orbit inclination) = 28° and the southern border of Germany is at 47° N

I have removed the section about the moon. The moon is irrelevant.

@BrianS But Germany isn't a space faring country... One can claim ownership of something while never going there.

@jwenting, Parties to the Moon Treaty are Australia, Austria, Belgium, Chile, Kazakhstan, Kuwait, Lebanon, Mexico, Morocco, Netherlands, Pakistan, Peru, Philippines, Saudi Arabia, Turkey, and Uruguay; additionally, France, Guatemala, India and Romania have signed but not ratified the treaty. Germany is not on either of those lists.

In the UK, you have rights up to about 1000 feet
According to In Brief (a free legal-information website written by legal experts)

The common law distinguishes between two different types of airspace. The lower and Upper stratum.
The lower stratum is concerned with the portion immediately above the land and interference with this air space would effect the landowner’s reasonable enjoyment of the land and the structures upon it.
  Wrongful intrusions include; Overhanging branches of a neighbours trees and plants or  projecting eaves or advertising signs and Booms of cranes being used for construction work on neighbouring land.
The Higher Stratum is something which exists above the height which is reasonably acceptable and necessary for the ordinary use and enjoyment of the land by it’s owner. The landowner has no greater rights to this airspace than any other member of the public.
S. 76 Civil Aviation Act 1982  states that ‘the lower stratum is unlikely to extend beyond an altitude of much more than 500 or 1,000 feet above roof level, this being roughly the minimum permissible distance for normal overflying by any aircraft’ (Rules of the Air Regulations 2007, Sch 1, s. 3(5)).

"unlikely to extend" - what a delightfully lawyerly hedge :-)

All that says is that planes cannot pass below 1000 to 500 ft (or os), and that just makes certain types of air traffic illegal in that space.  It doesn't necessarily give you rights to the air above your land (which isn't to say you don't have those rights, I'm more pointing out that this excerpt doesn't prove you do.)

@Jay, I've extended the quotation and provided a reference. A delivery drone in the lower stratum would constitute a "wrongful intrusion" on the landowners rights to reasonable enjoyment of their land. As always, anyone needing legal "proof" should consult the relevant legislation and a lawyer.

The phrase "lower stratum" does not seem to appear in UK legislation and certainly does not appear in s76 of the CAA 1982. I'll try to give a more complete answer.

I've posted an answer which I hope is clearer. I'm not particularly confident with In Brief's use of the legislation (eg the citation "s3(5)" is incorrect - suggesting someone unused to English statutory drafting wrote that bit).

Interesting question. In the US, it appears that the guiding principal is the FAA's definition of Navigable Airspace (another item borrowed from sailing?). And that definition is changing.
In general this is anything above 500 feet, but of course there are exceptions. This document provides some guidance.

There is some case law that states that your privacy extends up to 87.5'AGL  This was in application to a hovering 'drone'  flyovers for other purposes probably does not apply.  General flyovers of adjacent property would fall under the same rules and laws that govern manned aircraft overflight - FAA domain.  Privacy laws seem to be more narrow to hovering.  Expectation of privacy has many limitations.  eg. if the paparazzi can see you with their long range cameras, then you do not likely have much of an argument re privacy.  However if you have an 8' fence and there are no tall structures which allow a clear view, you might just have a claim - Property rights domain.

Can you provide some citation of where this case law came from?

I will look into.  Came in a general conversation at the recent FAA Symposium with some legal folk.

In the United States, air rights, especially with sUAS operation still remain vague and case law concerning them is not fully decided.  The most succinct ruling that I know of in the subject is United States v Causby, 328 U.S. 256 (1946).  Here the Supreme Court struck down the Heaven and Hell Doctrine, stating that navigable airspace over the United States was under the control and regulation of the Federal Government, not State or local governments nor property owners.  To do otherwise would be cause for countless tresspass lawsuits over overflying aircraft.  The Court, however, ruled for the defendant, citing that in his situation that the government had violated his 5th Amendment rights with low flying aircraft, stating that a property owner has ownership over airspace “within immediate reach”.  In the case of Causby, heavy bombers flying 85ft over his ranch on approach to an Army Air Field did create a tresspass.
The problem here in modern times is that “navigable air space” for SUAS lies between ground level and 400 feet AGL. Cosby never gave a definition specific to wear a landowners property rights ended and when navigable airspace began.  During the 1940s, it started at 500 feet AGL and as such is still remains vague to this day.
As a general courtesy, I will never over fly private property lower than 100 feet AGL, simply to give the landowners a little bit of space and not have the appearance of trust pass with flying a sUAS.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Light indication of a 2-bar system while on the correct glideslope?
I am trying to compare a VASI-4 light system with a PAPI lights. I know that 2White-2Red is the pattern that indicates that the aircraft is on the glideslope; more reds mean lower and more white means higher than the desired glideslope height. With relations to that, how should the VASI lights be on a correct/incorrect approach?
P.S. My question is specific to VASI-4 light system aka 2-bar VASI.
UPDATE I found this from FAA that may very well be the answer, but an explanation would be great.

@FreeMan        I didn't ask for how they work. I don't see this as a duplicate. I asked for the sources that confirms what the correct indication for 2-bar VASIs should be

The sources are contained in the answers of the other question.